Paper has been used in applications such as bags, wrapping paper, printing paper, photographic paper, and the like.
In general, specific applications require specific modifications in the paper making process to prepare a paper for that specific application.
For example, different additives are typically added to the fibers to improve the dry and wet strength of paper. Other substances are sometimes applied to the surface of the paper to impart water or grease proofing, or to render the paper bondable to other substrates such as a polyethylene plastic sheet.
In this context, it has been desirable to have paper whose composition would allow the sheets of the paper to have both good wet and dry strength.
It has also been desirable to have the same paper sheet exhibit barrier properties or be bondable to another substrate without coating the sheet with another substance such as an adhesive. Attempts have been made in the past to construct such a paper sheet.
Charles Snead and Ralph Peters in U.S. Pat. No. 2,976,205 describe the preparation of webs and sheets from cellulose esters. In this patent, the inventors disclose the use of 100% cellulose esters, primarily cellulose acetate, to form sheets. The sheets optionally could be treated with a plasticizer. Upon treatment with heat and pressure, the sheet became a transparent, homogenous sheet.
Similarly, Griggs et al., in U.S. Pat. No. 3,103,462, disclose a method for improving the strength characteristics of paper by including greater than 75% of a partially acetylated cellulose fiber and sizing the paper with classical sizing agents. Plasticizers were not considered, however.
The methods disclosed in U.S. Pat. Nos. 2,976,205 and 3,103,462 revolve around the "wet" process of classical paper making.
In U.S. Pat. No. 3,261,899, Coates describes a "dry" process for making synthetic fiber paper which involves web carding cellulose acetate stable fiber that has a length greater than 0.5 inch. optionally, the paper can contain natural fiber such as wood pulp. In the method of U.S. Pat. No. 3,261,899, the web is sprayed with a plasticizer and calendared in the temperature range of 65.degree. C. to 190.degree. C.
All of the methods described in U.S. Pat. Nos. 2,976,205, 3,103,462, and 3,261,899 have similar problems. All of these inventions disclose very high levels of cellulose Acetate which raises the costs of these synthetic papers relative to papers utilized in the market place.
The high level of cellulose acetate makes these "synthetic" papers more of a moldable plastic sheet rather than a classical paper sheet. That is, these sheets are not really suitable for conventional paper applications.
The inventors of these previous inventions desired to take advantage of the high cellulose acetate content of these papers and, recognizing the need for plasticization of cellulose acetate, attempted to add plasticizer to the synthetic papers. Unfortunately, the classical cellulose acetate plasticizers described in U.S. Pat. Nos. 2,976,205 and 3,261,899 are not convenient for use in classical paper making operations.
As will become apparent, one of the critical components of the present invention are alkylpolyglycosides (APG).
Alkylpolyglycosides are nonionic surfactants which have found widespread acceptance in a number of applications such as detergents, cosmetics, deinking agents, and the like.
Examples of the preparation of APG are disclosed in U.S. Pat. No. 5,138,046 (1992) to Wuest, Eskuchen, Wollmann, Hill, and Biermann; U.S. Pat. No. 4,996,306 (1991) to McDaniel and Johnson; U.S. Pat. No. 4,721,780 (1988) to McDaniel and Johnson; U.S. Pat. No. 5,104,981 (1992) to Yamamuro, Amau, Fujita, Aimono, Kimura; EP publication 0132043 (1984) to Davis and Letton; and EP publication 0387912 (1990) to Yamamuro, Koike, Sawada, and Kimura.
With regard to the use of APG as paper additives, Spendel, in EP Application A2 347176 (1989) and in U.S. Pat. No. 4,959,125 (1990), discloses tissue paper (paper towels and toilet tissues) consisting of wood pulp sprayed with a non-ionic surfactant (APG is preferred) and starch aqueous solutions. This combination gives improved softness and strength. The process for preparing such tissue paper is disclosed by Spendel in U.S. Pat. No. 4,940,513 (1990) and in EP Application A2 347177 (1989). Later, Phan et al., in U.S. Pat. No. 5,385,642 (1995) and in WO 94/26974 (1994), disclosed a process for treating tissue paper with a tri-component biodegradable softener composition, one component of which is an APG.
Similarly, Ampuluski and Trokhan, in U.S. Pat. No. 5,246,545 (1993), disclose a process for applying chemical additives (for example, APG) to a hot roll by spraying, evaporation of solvent from the roll, leaving a concentrated layer of the additives, and transfer of the layer to the dry web of tissue paper.
None of the above-mentioned references are related to or require the use of a cellulose ester.
With regard to the use of APG as paper coatings, Lang and Baird in U.S. Pat. No. 2,666,713 (1954) claim the product of the reaction between a carbohydrate, including alkyl glycosides, and an aldehyde, as an additive for paper, which will increase the absorbance of water by the paper.
Touey, in U.S Pat. No. 3,053,677 (1962), discloses that carbohydrate esters (for example, methylglycoside tetraacetate) can be blended with petroleum waxes and applied to paper as coatings.
The use of APG in conjunction with a cellulose ester is known. For example, Touey, in U.S. Pat. No. 3,008,472 (1961), discloses using methyl glycosdies as a hydroscopic agent and carrier for additives such as starch or calcium carbonate. The additives/agents are applied to cellulose acetate filter tow and upon exposure to high humidity, the additives bond to the tow.
In a related patent, Touey and Mumpower (U.S. Pat. No. 3,008,474 (1961)) describe dissolving carbohydrate esters in plasticizers or in an organic solvent, mixing in powder additives, and spraying the Solution onto cellulose acetate filter tow. In all of these applications, the APG serves strictly as a carrier and as an agent to absorb moisture.
While the above-mentioned references relate to combinations of cellulose fiber with cellulose acetate fiber, cellulose acetate fiber with APG, cellulose fiber with APG, or processes to make these combinations, none of these references have recognized the distinct advantages and uniqueness of the product of the present invention that results from paper containing cellulose acetate as a synthetic fiber, and APG as a paper additive, which functions both as a plasticizer and a coating and as a strength additive.
In the medical packaging field, medical paper used in medical packaging serves a very important function. The medical paper acts as a filter to remove particulates and microorganisms, while at the same time allowing gas and water vapor to enter and escape during the sterilization process.
A medical instrument, for example syringe, is placed in a plastic tray (typically polyethylene or modified polyester) and then the paper is sealed over the opening of the tray. The paper is pattern coated with an adhesive in such a manner that spaces on the sheet are not coated. This allows the paper to be adhered to the plastic while allowing gases to enter and leave the medical packaging during sterilization.
Because one side of the paper must be easily printed upon, the adhesive is typically applied to one side of the sheet and this application is made in a post paper making step.
In considering this process, it is evident that there is a need for an additive which can be added directly to paper during the paper making process as an aqueous based system. The combination of this paper and additive should provide a sheet without coating in a second step with an adhesive.
It would also be an advantage if the additive could be applied to one side of the paper. Alternatively, it would be desirable to add the additive directly to the paper making fiber prior to the actual paper making.
Therefore, it is an object of the present invention to provide a composition comprising cellulose, cellulose ester, and APG or a mixture of APG and polyether glycol.
It is a further object of the present invention to provide a paper comprising cellulose fibers, cellulose ester fibers, and APG or a mixture of APG and polyether glycol, in which the paper can optionally contain other paper additives.
The process for incorporating APG or a mixture of APG and polyether glycol in the paper composed of cellulose ester fiber and cellulose fibers, and the process of calendaring such paper to improve the strength of the paper, are also set forth.
It is another object of the present invention to use the synthetic paper according to the present invention as a thermoplastic sheet and as medical paper.